This invention relates to light-sensitive silver halide grains suitable for rapid development and extremely less in fogging and light-sensitive silver halide photographic materials containing said grains, and a method for preparing silver halide photograhic emulsions containing said grains, which are less fogging and have high sensitivity compared with the grain diameter.
In recent years, light-sensitive photograhic materials are required to improve various characteristics, and particularly, in the light-sensitive materials for color paper, etc., it has been required to have high aptitude for rapid processings which can result an image having high sensitivity and desired gradation with short time in order to improve efficiency of a developing processing step.
Further, as the high-sensitivity photographic emulsion used for light-sensitive materials for photography such as a film for X-ray, color negative film, etc., there has been employed primarily a silver iodobromide emulsion having relatively large grains.
As a high sensitivity emulsion, silver iodobromide emulsions containing 0 to 10 mol % of iodine are well known in the art. And, as the methods for preparing these emulsions, there have been known the methods in which pH condition and pAg condition are controlled such as the ammoniacal method, the neutral method, the acidic method, etc. and the mixing methods such as the single jet method, the double jet method, etc.
On the basis of these known techniques, in order to accomplish further higher sensitization, improvment of graininess, high sharpness and low fog, very precise technical means have been investigated and practically applied. In the silver iodobromide emulsion, studies have been made even about the emulsions controlled in concentration distributions of iodine within the individual silver halide grains, to say nothing of crystal habits and grain size distribution.
The most orthodox method for accomplishing photographic performances such as high sensitivity and low fog density is to improve the quantum efficiency of a silver halide. For this purpose, the knowledges about solid physics have positively been applied. The study having calculated theoretically the quantum efficiency and speculating about the effect of grain size distribution is disclosed in, for example, the pretext of Tokyo Symposium concerning Progress in Photography in 1980, entitled "Interactions between Light and Materials for Photographic Applications", on page 91. According to this study, it is predicted to be effective for improvement of quantum efficiency to prepare a monodispersed emulsion by narrowing the grain size distribution. In addition, for accomplishing sensitization of a silver halide emulsion, in the step of chemical sensitization as described hereinafter in detail, it may be considered resonable to estimate that a monodispersed emulsion would be advantageous for accomplishing efficiently high sensitivity while maintaining low fogging. The monodispersed emulsion is an emulsion in which grain size distribution of silver halide microcrystalline constituting the emulsion is extremely narrow and it is uniform in characteristics other than the grain diameter such as, for example, physical properties, photographic performances, etc. within the grains, and is suitable for obtaining high photographic performances.
For preparation of a monodispersed emulsion in industry, it is necessary to control the feeding rate of silver ions and halogen ions to the reaction system theoretically determined under sufficient stirring conditions, on the basis of pAg and pH strictly controlled, as disclosed in Japanese Provisional Patent Publication No. 48521/1979. The silver halide emulsions prepared under these conditions comprise the so-called normal crystal grains having (100) faces and (111) faces having either cubic, octahedral or tetradecahedral shapes at various proportions. And, higher sensitization has been known to be possible with such normal crystal grains.
For preparation of a monodispersed emulsion, various methods have further known, for example, as disclosed in Japanese Patent Publication No. 36896/1973, Japanese Provisional Patent Publication Nos. 99419/1979, 77737/1980, 49938/1983 and 46640/1984. As can be seen from these descriptions, since silver iodobromide has low solubility and slow in grain growing speed, ammonia has usually been employed as a silver halide solvent to obtain an emulsion having a large grain size.
Silver bromide or silver iodobromide has a property that progress of development is inherently slow so that it is difficult to correspond to rapid processing required for a color paper, etc. Thus, silver chlorobromide emulsion which has rapid in progress of development has preferably been used. Further, in the light-sensitive material forming an image on a reflective support such as a color paper, etc., it is important characteristics to express clean white and also extremely low in fogging is indispensable so that these facts make difficult to select an emulsion.
According to the above situation, as the light-sensitive material for forming an image on a reflective support, it is considered that a monodispersed silver chlorobromide emulsion which is, in particular, lowered the fogging is the most preferred one which comply with the objects. Since the silver chlorobromide is relatively high in solubility and has rapid in grain growth, it is not necessary to use a silver halide solvent during grain formation, and the preparation thereof has hitherto been carried out by the so-called boiling method wherein mixing a halide ion solution and a silver nitrate solution.
As a silver chlorobromide emulsion improved in characteristics, there has been disclosed in Japanese Patent Publication No. 72737/1980 a silver halide photographic material containing silver chlorobromide grains which comprise rhombododecahedron having (110) crystal face, but it cannot satisfy the presently required performances for a light-sensitive material. Further, by an emulsion comprising silver chlorobromide grains having conventionally known various crystal forms, satisfied performances could not be obtained.
Further, in addition to fogging and sensitivity, it has been required to more improve with respect to various characteristics such as stability during preservation, prevention of fogging during high-temperature preservation, and the like. According to the characteristics of the silver chlorobromide obtained by the conventional method, it has been difficult to satisfy these requirements.